Optical disc drive and optical pickup

Abstract

An apparatus for reading and / or writing data from / on a medium with a light beam includes: a light source for generating the light beam; an objective lens for focusing the beam onto the medium; a lens shift sensor for sensing how much the optical axis of the objective lens has shifted from that of the beam; a wavefront corrector, in which correcting elements are arranged as a two-dimensional array so as to locally correct the wavefront of the beam and to be driven independently of each other; a wavefront calculator for finding correlation between each coordinate on a cross section of the beam and the wavefront phase of the beam; a lens shift correction calculator for modifying the coordinate-wavefront phase correlation according to the output of the lens shift sensor; and a controller for controlling the wavefront corrector in accordance with the output of the lens shift correction calculator.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to an apparatus for optically reading and / or writing information (or data) from / on a given medium, and more particularly relates to an optical disc drive and an optical pickup each including a wavefront corrector for controlling the wavefront of a light beam. 2. Description of the Related Art Generally speaking, in an apparatus such as an optical disc drive for reading and / or writing information optically from / on a storage medium (e.g., an optical disc), a wavefront corrector such as a liquid crystal element or a deformable mirror is often provided along the optical path of an incoming light beam in order to compensate for aberrations caused by variations in the tilt and base material thickness (i.e., the depth of the data storage layer) of the optical disc. In this case, it is important to minimize the decrease in aberration correction ability due to the shift of the optical axis of an...

AI Technical Summary

Benefits of technology

In order to overcome the problems described above, preferred embodiments of the present invention provide an optical disc drive and an optical pickup that can make the wavefront correction precisely enough with the lens shift effects minimized and without using any special member for aligning the optical axes of the objective lens and light beam with each other.

According to various preferred embodiments of the present invention described above, the wavefront calculating means finds correlation between each coordinate of the light beam and the wavefront phase and the lens shift correction calculating means modifies the coordinate-wavefront phase correlation according to the magnitude of lens shift. And the wavefront correction control means controls the wavefront correcting means in accordance with the output of the lens shift correction calculating means. Thus, the wavefront can be corrected highly precisely without using any special member for lens shift correction.

Problems solved by technology

Then, the wavefront correction for compensating for the aberrations cannot be achieved appropriately.

Nevertheless, the response characteristic should decrease due to the increase in the weight of the movable part, the actuator should have a complicated structure so as to get connected to the wavefront corrector appropriately, the optical pickup of that type should have an increased thickness, and various other secondary problems should arise.

The more necessary it is to make the wavefront corrector realize high-precision correction, process a multi-segment wavefront correction pattern and work in multiple different aberration modes properly, the more difficult it is to minimize the unwanted decrease in aberration correction ability while avoiding all those problems at the same time.

Firstly, the lens shift correcting mechanism disclosed in Japanese Laid-Open Publication No. 11-96577 tends to increase the overall size and cost of the drive unintentionally.

Thus, the addition of such a lens shift correcting mechanism must complicate the overall drive excessively.

Secondly, in the arrangement using the second and third groups of electrodes as disclosed in Japanese Laid-Open Publication No. 2001-167470, the resultant wavefront correction accuracy and the number of types of correctible wavefronts are not enough.

In other words, it is difficult to cope with a wide range of lens shifts while maintaining sufficient wavefront correction accuracy.

Consequently, according to the technique of Japanese Laid-Open Publication No. 2001-167470, it is still difficult to reduce the lens shift effects sufficiently while coping with any of those various other aberrations flexibly enough.

Thirdly, the arrangement disclosed in Japanese Laid-Open Publication No. 2001-167470 cannot perform the wavefront correction precisely enough with respect to a very small lens shift.

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